Carbofuran is a carbamate insecticide widely used on crops and in rice fields throughout Thailand. Although it has been reported to have low toxicity on mammals, it frequently found to be highly toxic on aquatic animals. In this study, guppy Poecilia reticulata was used to examine effects of carbofuran on aquatic organism. The acute toxicity of carbofuran on guppy at 96 hours showed the LC₅₀ at 0.10 ppm, indicating its high toxicity to this fish species. Histopathology of carbofuran on guppy after short-term exposure and its recovery response were studied using histological and histochemical method. The guppies were exposed to carbofuran at 0.005, 0.01, 0.025, 0.04 and 0.05 ppm for 6, 24, 48, 72 and 96 hours. The results in gill, liver and kidney tissues showed histopathological changes. The recovery study showed that the lesions found in gill tissues were reversible while the lesions in liver and kidney tissues were irreversible. The lipid accumulation in liver of treatment group was significantly increased comparing with control groups (P<0.05). Moreover, long-term exposure to 0.04 ppm carbofuran for 5 months was conducted on guppy. The results on histopathology of gill, liver kidney and gonad tissues showed various histological alterations. The lipid accumulation was also significantly increased in the treatment group (P<0.05). The severity of histopathological effects of carbofuran found to be increase with time. The study of reproductive toxicity of carbofuran on human and wildlife is still limited. In this study, guppy was selected for an assessment of carbofuran effect during pregnancy. Reproductive capability of female guppy exposed to 0.05 ppm carbofuran was significantly reduced to 9.0±0.3 individuals per female. Similarly, live birth index significantly decreased to 92.46% and 77.58% in 0.01 ppm and 0.05 ppm treatment group, respectively. Moreover, survival of offspring at the 15th day after birth was significantly reduced to 90.68% and 68.18% in 0.01 ppm group and 0.05 ppm treatment groups, respectively (P<0.05). On the other hand, the pregnant period of female guppy was significantly increased in treatment groups (P<0.05). Significant findings on morphological abnormality of the offspring revealed that 2% of the newborn in 0.05 ppm treatment had two heads in one body. The result from this study suggested that carbofuran can damage fish tissues and can impair reproductive capability of female guppy and reduce live birth index and the first generation (F₁).